In recent years, the amount of user data stored by users in storage apparatuses is increasing rapidly pursuant to the development of the information society and, consequently, customer needs concerning the increase in capacity and improvement in efficiency of storage apparatuses are also growing from the perspective of cost reduction.
Under these circumstances, the dynamic provisioning function is being proposed in recent years as one function of the storage apparatus. The dynamic provisioning function is a function of presenting to a server a virtual logical volume (this is hereinafter referred to as the “virtual volume”) as a logical volume (this is hereinafter referred to as the “logical volume”) for reading and writing data, and dynamically allocating a storage area for actually storing data to the virtual volume according to the usage status of the presented virtual volume (refer to Japanese Patent Laid-Open Publication No. 2003-015915). According to this kind of dynamic provisioning function, there is an advantage in that the storage area in the storage apparatus can be used efficiently while presenting to the server a virtual volume having a capacity that is greater than the storage area in the storage apparatus.
With a storage apparatus equipped with this kind of dynamic provisioning function, a virtual volume to be presented to the server and a pool for allocating the actual storage area to the virtual volume are defined. When the storage apparatus receives a write request to the virtual volume from the server and a storage area is not allocated to the address position designated as the data write destination, it allocates an unused storage area in the pool to that address position, and writes data into the storage area. Meanwhile, when the server receives a read request for reading from the address position to which the storage area in the virtual volume has not been allocated, the storage apparatus sends “0” as read data to the server. The correspondence between the virtual volume and the actual storage area is managed with a management table.
A pool is configured from one or more logical volumes (these are hereinafter referred to as the “pool volumes”) configured from a tangible storage area (this is hereinafter referred to as the “real storage area” as appropriate). Although a pool volume can be added to the pool even in operation, once a pool volume is set as the configuration volume of the pool, it is not possible to delete that pool volume from that pool. Thus, in order to reduce the capacity of the pool, it is necessary to recreate the pool. Meanwhile, if the unused capacity of the pool runs short, it will not be possible to write data into an area to which the storage area in the virtual volume has not yet been allocated.
Incidentally, the dynamic provisioning function that is currently being provided by the Applicant does not allow a logical volume in a storage apparatus equipped with the dynamic provisioning function and a logical volume provided by another storage apparatus to the foregoing storage apparatus to be set as the configuration volume of the same pool. In addition, the dynamic provisioning function provided by the Applicant recommends unifying the characteristics of the pool volumes configuring the same pool in consideration of performance.